text: The velocity potential on the internal surface and all points inside V (or on the lower surface S) is 0.
  The Doublet Strength is:
  The velocity potential on the outer surface is normal to the surface and is equal to the freestream velocity.
  These basic equations are satisfied when the geometry is a watertight geometry.  If it is watertight, it is a well-posed problem.  If it is not, it is an ill-posed problem.